A rolling bearing might be used in an environment where water can easily intrude into a bearing. For example, a rolling machine in steel facilities is a facility for mainly rolling a steel plate, and a rolling bearing for rotatably supporting a roll is used in a roll neck part of a rolling roll. In general, a multi-row tapered or cylindrical roller bearing is used. At rolling, since a large quantity of rolling water is supplied with the purpose of lubrication and cooling between a rolling roll and a rolled material, a periphery of the bearing of the roll neck part is in a use environment surrounded by a large quantity of rolling water. Since the supply of rolling water is usually a harsh condition for a seal device for waterproof attached to a bearing, housing or the like, it is difficult to completely prevent intrusion of rolling water into the bearing.
Also, since abrasion powder caused by contact between the rolling roll and a rolled material or scale falling from the rolled material and the like reaches a seal part with the large quantity of rolling water, it is a condition in which the seal itself can be worn easily. Therefore, it is difficult to completely prevent intrusion of the rolling water into the bearing by a seal device and the like.
Moreover, in the rolling roll, abrasion is caused on its surface by contact or friction with the rolled material as use progresses. Thus, when the roll is used for about several hours, it is removed with the bearing on from the rolling machine main body and replaced with a repaired rolling roll (with bearing on). The rolling roll removed from the rolling machine is repaired such as polishing on the surface with regard to the roll, but the attached bearing is not maintained or the like in usual.
A period from when the rolling roll is removed till when it is reused might reach several days depending on the number of rolling rolls in stock or operating state of the facility. That is, the bearing might be left for several days in a state with the rolling water intruding inside. Thus, so-called “season rust” might occur inside the bearing. Since the rolling roll is usually placed horizontally (laterally placed), the rolling water can easily remain at a lower part of an outer ring raceway surface and the rust can easily occur particularly on the outer ring raceway surface of that portion and the surface of a rolling element located at that portion. Also, such season rust can easily occur when the rolling machine of the steel facilities is stopped for a long time.
If such season rust occurs, not peeling life from inherent material fatigue but life caused by peeling starting at the rust on the surface becomes predominant in the bearing life, which makes the life short. Also, the bearing with the season rust developed has such damages with a high probability and has a short life. If such damage occurs during rolling, dimensional accuracy or appearance of the rolled material is adversely affected naturally and its cost burden becomes huge.
As the bearing at the roll neck part of such rolling machine, a tapered roller bearing or cylindrical roller bearing are used with a single- or multi-row. Particularly, a tapered roller bearing with four rows on one side is used in many cases.
Moreover, steel continuous casting facility, for example (hereinafter described as continuous caster in some cases), is a facility for manufacturing a steel plate product called slab/billet/bloom. A peripheral environment of a bearing supporting its guide roll (some have axle box) becomes a high temperature since a red-hot cast piece in a solidification process passes the vicinity of the bearing. Also, cooling water supplied for cooling the cast piece becomes a high-temperature steam (the cooling water is immediately changed to steam due to the high-temperature environment), and the environment is surrounded by the high-temperature steam. Also, the bearing might be directly splashed with the cooling water.
Thus, in a seal provided at the bearing of the guide roll part or the seal provided at the axle box, it is difficult to completely prevent intrusion of moisture such as steam and cooling water into the bearing. Also, the seal itself can easily wear due to the high-temperature environment.
The continuous caster is usually stopped for several days a month for facility inspection. At this time, the season rust can easily develop similarly to the bearing of the roll neck part of the above-mentioned rolling machine. If the facility is operated again with the season rust developed, peeling with the rust as a starting point is caused. Also, in the case of need to repair due to abrasion of the roll and the like in the continuous caster, an entire unit called segment constituted by a plurality of rolls is replaced. The bearing used in the replaced segment is overhauled and those without damage or the like are reused. However, if it is left for a long time till overhaul, the season rust might occur at the outer ring raceway surface and the rolling element similarly to the bearing at the roll neck part of the rolling machine. Those with the season rust developed are required to be replaced, which makes a factor to increase the cost.
In these continuous casters, self-aligning roller bearing or a tapered roller bearing, cylindrical roller bearing provided with an aligning housing ring at the outer ring or inner ring are used in many cases.
From the above, in order to reduce costs such as repairing cost of the bearing, bearings resistant against rust are in demand.
In order to suppress development of the season rust, means of mounting double and triple seals to prevent intrusion of water by sacrificing a load capacity of the bearing, which makes a main factor in rolling fatigue life, means of applying chemical conversion treatment such as phosphate coating on the whole surface of the bearing, means of forming a metal coating made of zinc and the like by electric plating and the like have been employed.
In the bearing used in the rolling machine and continuous caster, other than the above problem of the season rust, there is a following problem relating to the damage of the bearing. That is, if the rolling water and the like intrude into the bearing during use, a lubrication state is deteriorated, the rolling element slips on the raceway surface, and the raceway surface and the surface of the rolling element might be damaged. The damage modes are represented by abrasion, peeling, smearing and surface damage called galling.
For example, rolling might be conducted in the rolling machine while rapid acceleration/deceleration are repeated at a rolling velocity in a range from approximately 100 m/min to approximately 2500 m/min. Moreover, the rolling machine is used in a wide range of conditions from a low speed to a high speed or from a light load to a heavy load such that an impact load is applied when the rolled material enters between the rolls, a heavy load is applied exactly when the rolled material is passing between the rolls, and rotation might be under a light load condition that slip occurs at a roller of the bearing after the rolled material has passed between the rolls. Thus, if water intrudes into the bearing and the lubrication state inside the bearing is deteriorated, damage such as peeling, smearing, galling and the like might occur depending on the use condition and the like. For example, in the use under the condition of high speed and heavy load, peeling or galling caused by oil film shortage easily occurs, in the use under the condition of high speed and light load, smearing caused by slide of a roller can easily occur, and in the use under the condition of low speed and heavy load, abrasion easily occurs.
These problems also apply to the bearing of a facility used around the continuous caster or rolling machine. For example, the same applies to the bearing of a table roller installed before and after the rolling roll of the rolling machine. As the bearing of the table roller, a cylindrical roller bearing provided with an inner ring or outer ring in the form divided into two parts is used in many cases.
As a solution to these problems, improvement of a material resistant to damage on the surface such as abrasion and the like has been proposed as described in Patent Document 5.
However, in the case of the roll neck bearing in the rolling machine operated under the harsh condition, even if a seal to prevent intrusion of water is mounted, it is not always possible to completely prevent the water intrusion, and prevention of rust development even if water intrudes is in demand.
Also, since a chemical conversion coating such as manganese phosphate coating and the like is a corrosion coating, it corrodes a base material to some degree. Thus, if the chemical conversion coating is applied on the raceway surface of the bearing, peeling occurs from that portion as a starting point depending on the degree of the corrosion, and duration of life is reached earlier than rust development life in the case where chemical conversion coating is not applied in some cases.
Moreover, in a method by electroplating or chemical plating, if the base material is steel, hydrogen intrudes into the steel product in a plating process, reduction or management of a possibility to cause local hydrogen embrittlement is difficult, and it is hard to ensure sufficient reliability of the rolling device.
Moreover, in the chemical conversion coating, if a degree of corrosion into the base material is to be reduced, a crystal size of the coating is affected, and the chemical conversion coating becomes easy to drop due to rolling. As a result, an oil maintaining power is lowered and the like after the rolling and rust development life cannot be elongated, which is a problem.
Moreover, in the electroplating or chemical plating method, acid cleaning as pre-treatment and baking as post-treatment cannot be avoided. Therefore, labor and costs are tremendous for process control to minimize hydrogen intrusion into the steel product in the acid cleaning process and thermal influence on the thermally treated steel product due to baking and moreover, process control including treatment of discharged water and the like used for the plating.
Moreover, in the electroplating or chemical plating method, as a feature specific to the plating, a micro defect such as a pinhole and the like can be easily formed on a plated layer, and without forming a relatively thick coating in order to prevent this defect, a sufficient rust-proof effect cannot be obtained easily. However, with the relatively thick coating, the plated layer itself can be easily peeled off and moreover, there is a problem that ensuring of bearing accuracy such as a gap inside the bearing and the like becomes difficult.
According to molten metal plating, the above problems of waste water and the like are fewer, but since treatment at a melting point or above of the metal forming the coating is indispensable, thermal influence on the steel product as the base material is unavoidable, and tempering or dimensional change of the thermally treated steel product can easily occur. Also, since the molten metal plating has a relatively thick coating, peeling-off or dimensional change easily occurs.
Thus, the present invention solves the problems as above of the prior art and has an object to provide a rolling device in which rust development or damage on the raceway surface or rolling surface hardly occurs even if water and the like intrudes.    Patent Document 1: JP-A-2002-106588    Patent Document 2: JP-A-2003-239992    Patent Document 3: JP-A-09-329147    Patent Document 4: JP-A-11-132229    Patent Document 5: JP-A-10-184700    Patent Document 6: JP-A-05-240256    Patent Document 7: JP-A-2002-139052    Patent Document 8: JP-A-2002-147473